Generally, in a mobile communication system, a user equipment is able to receive information in downlink from a base station. And, the user equipment is able to transmit information in uplink as well. The information transmitted or received by the user equipment includes data and various kinds of control information. And, various physical channels exist according to a type usage of the information transmitted or received by the user equipment.
FIG. 1 is a diagram for explaining physical channels used for such a mobile communication system as 3GPP (3rd generation partnership project) LTE (long term evolution) system and a general signal transmitting method using the physical channels.
Referring to FIG. 1, in a step S101, a user equipment, of which turned-off power is turned on again or which enters a new cell, performs an initial cell search for matching synchronization with a base station or the like. For this, the user equipment matches the synchronization with the base station by receiving a primary synchronization channel (P-SCH) and a secondary synchronization channel (S-SCH) from the base station and then obtains such information as cell ID and the like. Subsequently, the user equipment is able to obtain intra-cell broadcast information by receiving a physical broadcast channel from the base station. Meanwhile, the user equipment is able to check a downlink channel status by receiving a downlink reference signal (DL RS) in the initial cell searching step.
Having completed the initial cell search, the user equipment is able to obtain further detailed system information by receiving a physical downlink control channel (PDCCH) and a physical downlink shared channel (PDSCH) according to the physical downlink control channel information.
Meanwhile, the user equipment failing to complete the access to the base station is able to perform such a random access procedure as the steps S103 to S106 to complete the access to the base station. For this, the user equipment transmits a feature sequence as a preamble via a physical random access channel (PRACH) [S103] and is then able receive a response message in response to the random access via a physical downlink control channel and a physical downlink shared channel corresponding to the physical downlink control channel [S104]. Subsequently, in case of a contention based random access except a case of handover, it is able to perform such a contention resolution procedure as a transmission of an additional physical random access channel [S105] and a reception of a physical downlink control channel and a physical downlink shared channel corresponding to the physical downlink control channel [S106].
Having performed the above procedures, the user equipment is able to perform general uplink/downlink signal transmitting procedures including a physical downlink control channel/physical downlink shared channel reception [S107] and a physical uplink shared channel/physical uplink control channel (PUSCH/PUCCH) transmission [S108].
FIG. 2 is a diagram for explaining a signal processing method for transmitting an uplink (UL) signal from a user equipment.
Referring to FIG. 2, in order to transmit a UL signal, a scrambling module 201 of a user equipment is able to scramble a transmission signal using a user equipment specific scrambling signal. This scrambled signal is inputted to a modulation buffer 202 to be modulated into a complex symbol by BPSK, QPSK or 16 QAM according to a type of the transmission signal and/or a channel status. Subsequently, the modulated complex symbol is processed by a transform precoder 203 and is then inputted to a resource element mapper 204. The resource element mapper 204 is able to map the complex symbol to a time-frequency resource element that will be used for real transmission. This processed signal enters a SC-FDMA signal generator 205 and is then transmitted to a base station via an antenna.
FIG. 3 is a diagram for explaining a signal processing method for transmitting a downlink (DL) signal from a base station.
Referring to FIG. 3, in 3GPP LTE system, a base station is able to transmit at least one or more code words in DL. Therefore, each of the at least one or more code words can be processed into a complex symbol through a scrambling module 301 and a modulation mapper 302 like the UL case shown in FIG. 2. Subsequently, the complex symbol is mapped to a plurality of layers by a layer mapper 303. Each of the layers can be assigned to each transmitting antenna by being multiplied by a prescribed precoding matrix selected according to a channel status by a precoding module 304. This processed transmission signal per antenna is mapped to a time-frequency resource element that will be used for transmission by a resource element mapper 305, is inputted to an OFDMA signal generator 306, and is then transmitted via a corresponding antenna.
FIG. 4 is a diagram for explaining SC-FDMA for UL signal transmission and OFDMA for DL signal transmission in a mobile communication system.
Referring to FIG. 4, a user equipment for UL signal transmission and a user equipment for DL signal transmission are identical to each other in including a serial-to-parallel converter 401, a subcarrier mapper 403, an M-point IDFT module 404 and a CP (cyclic prefix) adding module 406.
However, the user equipment for transmitting a signal by SC-FDMA further includes a parallel-to-serial converter 405 and an N-point DFT module 402. In this case, the N-point DFT module 402 is characterized in enabling a transmission signal to have a single carrier characteristic by partially canceling out IDFT processing influence of the M-point IDFT module 404.
MIMO is the abbreviation of multiple-input multiple-output. By doing away with using one transmitting antenna and one receiving antenna, the MIMO is the method of raising transceived data efficiency using multiple transmitting antennas and multiple receiving antennas. In particular, according to the MIMO technology, a transmitting or receiving side of a wireless communication system uses multiple antennas to increase capacity or enhance performance.
In order to receive one whole message, the MIMO technology applies a technique of completing the received whole message by gathering data fragments received via plural antennas together without depending on a signal antenna path. Since the MIMO technology is able to enhance a data transmit speed (data rate) within a specific range or is able to extend a system range for a specific data transmit speed, it is the next generation mobile communication technology widely usable for a mobile communication terminal, a real and the like. Many attentions are paid to this technology to overcome the traffic overcome of mobile communication that reaches a critical situation due to data communication expansion and the like.
FIG. 5 is a block diagram of a general MIMO communication system.
Referring to FIG. 5, if the number of transmitting antennas and the number of receiving antennas are simultaneously incremented into NT and NR, respectively, channel transmission capacity is theoretically increased in proportion to the number of antennas unlike the case that either a transmitter or receiver uses plural antennas. Therefore, it is possible to raise a data rate and to dramatically enhance frequency efficiency. The data rate according to the increase of the channel transmission capacity can be theoretically raised by an amount resulting from multiplying a maximum data rate R0 of the case of using one antenna by an increase rate R, of Math FIG. 1.
MathFigure 1Ri=min(NT,NR)  [Math.1]
For instance, in MIMO communication system using 4 transmitting antennas and 4 receiving antennas, it is able to obtain a data rate 4 times greater than that of a single antenna system theoretically. After the theoretical capacity increase of the multiple antenna system has been proved in the mid-90s, many efforts are ongoing to be made to research and develop various technologies to realize the substantial enhancement of data rate. And, standards of the 3rd generation mobile communication and various wireless communications have already reflected some of these technologies.
Looking into the current MIMO relevant study tendency so far, many efforts are ongoing to be made to the information theory study relevant to MIMO communication capacity calculation in various channel configurations and multiple access environments, radio channel measurement and modeling study in MIMO communication system, spatiotemporal signal processing technology study for transmission reliability and data rate enhancements and the like in various aspects.
The MIMO technology can apply to spatial multiplexing scheme, antenna diversity scheme and the like.
First of all, the spatial multiplexing is the scheme of transmitting different signal series via transmitting antennas, respectively. In this case, signals respectively transmitted via the transmitting antennas are received in a manner of being overlapped with each other. A receiver then separates the overlapped signals by ML (maximum likelihood) scheme, BLAST (Bell labs layered space-time) scheme, ZF (zero forcing) scheme, MMSE (minimum mean square error) scheme or the like. Moreover, in case that channel information is already known, it is able to transmit a signal in a manner of forming orthogonal beam by giving an appropriate weight to each transmitting antenna using the channel information. By this method, it is able to increase data transmit capacity using the spatial multiplexing.
Secondly, the antenna diversity is the scheme of transmitting or receiving one signal series via multiple antennas. In such manner, it is able to raise SNR (signal-to-noise power ratio). If a channel status is unstable, the antenna diversity is useful to cope with fading to enhance error rate performance.